In vivo characterization of chick embryo mesoderm by optical coherence tomography-assisted microindentation.

Embryos are growing organisms with highly heterogeneous properties in space and time. Understanding the mechanical properties is a crucial prerequisite for the investigation of morphogenesis. During the last 10 years, new techniques have been developed to evaluate the mechanical properties of biological tissues in vivo. To address this need, we employed a new instrument that, via the combination of micro-indentation with Optical Coherence Tomography (OCT), allows us to determine both, the spatial distribution of mechanical properties of chick embryos, and the structural changes in real-time. We report here the stiffness measurements on the live chicken embryo, from the mesenchymal tailbud to the epithelialized somites. The storage modulus of the mesoderm increases from (176 +/- 18) Pa in the tail to (716 +/- 117) Pa in the somitic region (mean +/- SEM, n = 12). The midline has a mean storage modulus of (947 +/- 111) Pa in the caudal (PSM) presomitic mesoderm (mean +/- SEM, n = 12), indicating a stiff rod along the body axis, which thereby mechanically supports the surrounding tissue. The difference in stiffness between midline and presomitic mesoderm decreases as the mesoderm forms somites. This study provides an efficient method for the biomechanical characterization of soft biological tissues in vivo and shows that the mechanical properties strongly relate to different morphological features of the investigated regions.